Ok, I need a little help here. I just pulled a error code 26. The check engine light came on when the truck was idling at a stop light waiting for traffic. Here's some info on the truck. I don't know when the oxygen sensor was changed last and the truck burns coolant very slowly. I don't notice any smoke coming out the tailpipe.

Plan of attack?

stock 92 pickup, v6, xtra cab, 4x4 IFS, 204k miles